The present invention relates to a metallic plate material for a shadow mask used in a color picture tube, which is designed to improve the adhesion between the plate material and a photoresist and also the adhesion between the plate material and a negative pattern in the shadow mask producing process, thereby reducing the suction time required to bring the negative pattern into contact with the plate material, and thus enabling an improvement in the productivity, the plate material also permitting the negative pattern to be transferred accurately and causing no annealing adhesion in the shadow mask softening annealing step in the process of producing a color picture tube.
Hitherto, shadow masks for color picture tubes have been formed using a low-carbon, aluminum-killed, cold-rolled steel plate consisting essentially of iron or an alloy plate consisting essentially of iron and nickel, for example, a 36 nickel-iron invariable alloy plate. As to these plate materials, no precise definition of the surface roughness has been made particularly.
Since there is no precise definition of the surface roughness of the conventional plate materials for shadow masks, as stated above, the adhesion between a metallic plate material and a photoresist is likely to become unstable in the process of producing a shadow mask from the plate material used as a blank, and the adhesion between a negative pattern and the metallic plate material coated with the photoresist is also unstable in the step of transferring the negative pattern. In addition, annealing adhesion occurs in the step of subjecting the resulting shadow mask to softening annealing to give press deformability thereto in the process of producing a color picture tube, thus having adverse effects on the quality and the productivity.